DETECTION OF CNS DISEASE

Abstract: Techniques for the detection of disease of the central nervous system, particularly of bovine spongiform encephalopathy "mad cow disease", scrapie and related states, are provided based upon the detection of a factor present in the urine of affected animals or humans. That factor is defined in terms of elution data from an ion exchange column and by electrochemical characteristics.

Description: DETECTION OF CNS DISEASE. The present invention relates to techniques for the detection of disease of the central nervous system, particularly bovine spongifor encephalopathy, scrapie, Jacob-Creuzfeld syndrome and related states. It has been noted that serotonin levels are reduced in the blood of scrapie infected sheep (Chatelain et al (1984) CR Soc. Biol. 1I8_, 664-670, and that some electrochemical changes occur in the urine of such sheep (Combrisson et al (1991) Bull. Acad. Vet. de France 6jt, 257-266; Banissi-Sabourdy et al (1992) Bioelectrochem & Bioenergetics 28. 127-147, but no reliable test has resulted from these findings. At present there is no diagnostic test available for the screening of animals, including humans, for spongiform encephalopathy type disease and the confirmation of its presence is usually by direct observation of tissues in autopsy. There remains a particular need for a method of screening live animals, particularly prior to slaughter for consumption purposes, and preferably before their milk is consumed, and most preferably for a non-invasive test. The present inventor has now identified a factor present in the biological fluids of affected animals, particularly their urine, the amount of which correlates well with the occurence of these diseases. The present invention provides a method for determining the presence of central nervous system disease in a human or animal body by analysis of one or more of its biological fluids characterised in that the fluid is analysed for the presence of a factor associated with a fraction obtainable from an ethanol extract of urine from animals having the disease, that fraction being elutable from a 0.2M Tris buffer pH 7-0 equilibrated DEAE-Sepharose CI ion exchange column (particularly a CL6B) increasing gradient elution using from 0 to 0.2M sodium chloride in 0.02M Tris buffer pH 7-0; the fraction being elutable with between O.OδM and 0.015M sodium chloride, particularly between O.OδM and 0.09M sodium chloride in Tris buffer pH7.0; wherein the amount of this factor is related to presence of the disease state. The most convenient method for detecting this 'disease' factor may of course vary depending upon the fluid to be tested, eg. whether CSF fluid, whole blood or a fraction thereof, or urine. The sampling of urine renders the test suitable for routine screening by electro -chemical detection means and can avoid the need for invasive methods. Other tests, eg. colorimetric and immunological, will also be applicable. A preferred aspect of the present invention relates the amount of the 'disease factor' with the amount of one or more reference factors present in the fluid, particuarly in urine, and uses the ratio of these to indicate disease presence. These reference factors are a reference factor (2) that is associated with a fraction elutable with between 0.09 and 0.13M sodium chloride, and a reference factor (3) associated with a fraction elutable with between 0.13 and 0.2M sodium chloride; both using the ion-exchange column technique described above and the same ethanol extract of disease animal's urine. The second reference factor (3) has been found to be uric acid, the first reference factor (2) has been found to have properties associated with tyrosine or a precursor or derivative thereof having at least one, and possibly two or three, phenolic groups including one phenol group para to a substitute side chain. It should be realised that the amount of material isolatable from urine is very small and has so far proven difficult to identify. The disease factor (1) has been found to have properties consistent with having a substituted phenyl or histidine nucleus, also with a para-hydroxy substituent and at least one methyl substituent. Both disease factor (1) and reference factor (2) have similar physical properties. Both are water soluble and soluble in methanol and ethanol, both are bound to aminopropyl solid phase extraction columns but only reference factor (2) can be desorbed using 0.5 HC1 in 50:50 methanol/water; thus in this way reference factor can be separated from disease factor. The disease factor does not come off this column in either 100# methanol or 1:1 methanol:5M HC1 in water. Both reference factor (2) and disease factor (1) are bound to anion exchange material such as DEAE-Sepharose, being eluted with between 0.08 to 0.15M sodium chloride, the reference factor being desorbed slightly after the disease factor, ie. above 0.09M as described above. The reference factor (2) may be further identified by its Rf factor on TLC RP18 plates using an 80:20 water:methanol solvent. It has been found that measurement of the difference in height of an electrochemically measured peak obtained relating to the amount of reference factor (2) and one obtained relating to the disease factor, divided by the difference in height of peaks relating to the reference factors (2) and (3) . provides a value indicative of disease state. Initial investigation shows that values of 1.0 or more correlate with absence of disease while less than 1.0 correlates with disease status. It will be appreciated that any method that measures the relative concentrations of disease factor and one or both of these reference factors may be used to indicate presence of the aforesaid diseases. Furthermore, it will be realised that in some disease formats, the disease factor may occur in an altered form while still retaining its basic chemical characteristics; eg. as a conjugate or metabolite. Such variations of the factor will also be targetable for the purposes of detection and thus the present invention relates to their targeting in so far as they are so related and correlate to the diseases of interest. In a further aspect of the present invention there is provided a test kit for determining the presence of central nervous system disease comprising one or more reagents capable of specifically detecting the disease factor described above. Most conveniently these agents will be specific binding assay agents capable of specific detection of the approximate amount of the disease agent in a biological fluid. Typically such agents will be antibodies raised to immunogens formed from the purified fraction obtained by its elution from a column, eg using 0.08 to 0.09M NaOH in 0.02M Tris buffer from a DEAE column as described above. Such antibodies may be monoclonal antibodies or polyclonal antibodies raised in the known manner using suitably selectable immunogen design, eg ovalbumen conjugate, and adjuvant if necessary as will be determined by simple bench experimentation; the antibodies being conventionally labelled for detection of disease agent in the known manner. Alternatively the test reagents may include specific chemical test agents for the agent. Isolation of the fraction containing the disease factor and the application of electrochemical techniques to the method of the invention will be illustrated by way of the non-limiting examples and related Figures provided below. FIGURES Figure 1: shows a voltammogram of a sample derived from BSE positive urine as obtained using the method of Example 1. Figure 2: shows a voltammogram of a sample derived from BSE negative urine as obtained using the method of Example 1. EXAMPLE 1. Urine samples were taken from animals (cattle) under investigation and screened using a commercial electrode cell (ESA Analytical: Coulochem II, 5010 electrode assembly) containing three porous carbon electrodes, these being a reference electrode, a working electrode and a secondary electrode. The sample was prepared by mixing 200μl of urine with 768 μl deionised water and 32 μl hydrochloric acid (10.8N) (or concentrated sulphuric acid) in order to acidify it prior to introduction into the electrode cell. The cell was operated using the following electrical parameters: Applied potential cycles : ( i ) 175 mV to 1325 mV ( ii ) 1325 mV to 175 mV These cycles were repeated one or more times and the voltage change rate used was usually 10 mV/second, although any rate in the range eg. 1-100 mV/second was found to be usable. The induced current was measured at 20 μamps full scale deflection but 2-200 μamps f.s.d. may be conveniently used. The output of the cell electrodes was transcribed to a X-Y linear plotter. Results: three peaks were produced on the plotter output; (a) Primary Peak 1: occurs only on the second and subsequent cyclic sweeps during increasing applied voltage between 650 and 850 mV (mean at 750 mV) ; this being referred to also as disease correlating peak. (b) Reference Peak 2: occurs only on the second and subsequent cyclic sweep during increasing applied voltage at approximately 100 mV lower than the Primary Peak 1. (c) Reference Peak 3: occurs only on the first cyclic sweep during increasing applied voltage at approximately 25 to 100 mV higher than the Primary Peak 1, this being resultant from irreversible oxidation and being found to correspond to uric acid. Quantitation: The Primary Peak 1 is found to be increased in the diseased state but because urine from different animals, whether captured mid-flow, by cannula or from post-mortem bladders, varies considerably in concentration/dilution, Reference peaks 2 and 3 were used to normalise readings by serving as internal standards relating to urine dilution within the sample. Thus the difference in height of the Primary Peak 1 and Reference Peak 2 divided by the difference in height of the Reference Peaks 2 and 3. provides a determining numerical value indicative of disease state: Peak 2 - Peak 1 greater than or equal to 1.0 Sample Negative Peak 3 - Peak 2 Peak 2 - Peak 1 less than 1.0 - Sample Positive Peak 3 - Peak 2 Assessment of test: A trial was run using blind samples analysed by the test as described above and the results compared to histopathological diagnosis results, the results of which are provided in Table 1 wherein positive identifications of disease state are indicated by + and negative identifications by -. TABLE 1 Sample Urine Histol Sample Urine Histol 1 + + 10 _ _ 2 - - 11 + + 3 + + 12 + + 4 */- + 13 + + 5 + + 14 + + 6 - - 15 + + 7 + + 16 + + 8 + + 17 + + 9 + + 18 + + EXAMPLE 2. Urine from diseased cattle was subjected to a number of isolation procedures to provide purified fractions containing the identified disease correlating factor. One preferred procedure is as follows: (a) Ethanol extraction: Inorganic salts and ethanol insoluble compounds were precipitated from urine by addition of 4 x volume of absolute ethanol and filtering off the precipitate. The filtrate was evaporated to dryness and the compounds of interest redissolved in ethanol, evaporated to dryness again and taken up in 0.02M Tris buffer at pH 7.0 for a separation stage (b) . (b) The sample from step (a), obtained from 0 ml of urine, was absorbed onto a DEAE-Sepharose CL6B (Pharmacia) ion exchange column previously equilibrated with 0.2M Tris buffer pH 7-0. The column was washed clear of non-adsorbing material and subjected to an increasing gradient elution from 0 to 0.2M sodium chloride in 0.02M Tris buffer pH 7.0. 4ml fractions were collected and assessed for activity on the electrochemical detector. Peak 1 was eluted between 0.08 and 0.09M sodium chloride and found to be essentially electrochemically pure. Peak 2 was eluted at between 0.09 and 0.13 sodium chloride and was also found to be electrochemically pure. Peak 3 was eluted at between 0.13 and 0.2M sodium chloride. The exact elution salt concentration required appears to depend on the amount of original urine and its original concentration.

Claims: CLAIMS . 1. A method for determining the presence of central nervous system disease in a human or animal by analysis of one or more of its biological fluids, characterised in that the fluid is analysed for the presence of a disease factor associated with a fraction obtainable from an ethanol extract of urine obtained from animals having the scrapie or Bovine spongiform encephalopathy, that fraction being elutable from a 0.2M Tris buffer pH 7.0 equilibrated DEAE-Sepharose CI ion exchange column by increasing gradient elution using from 0 to 0.2M sodium chloride in 0.02M Tris buffer pH 7.0; the fraction being elutable with between 0.08 and 0.09M sodium chloride in Tris buffer pH 7.0; and that the amount of this factor is related to presence of the disease state. 2. A method as claimed in claim 1 wherein the amount of the disease factor (1) is compared with the amount of a reference factor (2) that is associated with an ethanol extractable urine fraction elutable from a 0.2M Tris buffer pH 7.0 equilibrated DEAE-Sepharose CI ion exchange column, using increasing gradient elution from 0 to 0.2M sodium chloride in 0.02M Tris buffer pH 7-0; the fraction being elutable with between 0.09 and 0.13M sodium chloride. 3- A method as claimed in claim 1 or claim 2 wherein biological fluid analysed is urine and the amount of the disease factor is compared with the amount of a reference factor (3) that is associated with an ethanol extractable urine fraction elutable from a 0.2M Tris buffer pH 7.0 equilibrated DEAE-Sepharose CI ion exchange column, by increasing gradient elution using from 0 to 0.2M sodium chloride in 0.02M Tris buffer pH 7.0; the fraction being elutable with between 0.13 and 0.2M sodium chloride. 4. A method as claimed in claim 3 wherein the reference factor (3) is uric acid. 5. A method as claimed in claim 3 characterised in that the difference in height of an electrochemically measured peak obtained relating to the amount of reference factor (2) and that obtained relating to the disease factor (1), is divided by the difference in height of peaks relating to the reference factors (3) and (2), and the value obtained is used to determine disease state. 6. A method as claimed in any one of the preceding claims wherein the disease is bovine spongiform encephalopathy, scrapie, Jacob-Creuzfeld syndrome or a related disease state. 7. A method as claimed in claim 1 wherein the disease factor has properties consistent with its having a substituted phenyl or histidine nucleus with a para-hydroxy substituent and at least one methyl substituent. 8. A method as claimed in claim 1 or 7 wherein the disease factor is soluble in water, methanol and ethanol and is bound to aminopropyl solid phase extraction columns. 9. A method as claimed in claim 8 wherein the disease factor is not recoverable from an aminopropyl solid phase extraction column using 100# methanol or 5 aqueous HCl/methanol 1:1 mixture as eluant. 10. A method as claimed in any one of claims 2 to 7 wherein reference factor (2) has properties associated with tyrosine or a precursor or derivative thereof having at least one phenolic group including one phenol group para to a substitute side chain. 11. A method as claimed in any one of claims 2 to 7 or 9 wherein reference factor (2) is soluble in water, methanol and ethanol and is bound to aminopropyl solid phase extraction columns. 12. A method as claimed in claim 10 wherein reference factor (2) is recoverable from an aminopropyl solid phase column using 0.5M HC1 in 50:50 methanol/water. 13. A method as claimed in any one of claims 1 to 12 wherein the ion exchange column used for the elution of disease factor (1) or reference factor (2) is a DEAE-Sepharose CL6B. 14. A test kit for determining the presence of central nervous system disease comprising one or more reagents capable of specifically detecting a disease factor associated with a fraction obtainable from an ethanol extract of urine obtained from animals having scrapie or Bovine spongiform encephalopathy, that fraction being elutable from a 0.2M Tris buffer pH 7.0 equilibrated DEAE-Sepharose CI ion exchange column by increasing gradient elution using from 0 to 0.2M sodium chloride in 0.02M Tris buffer pH 7-0; the fraction being elutable with between 0.08 and 0.09M sodium chloride. 15. A test kit as claimed in Claim 14 wherein the reagents comprise specific binding assay agents capable of binding to the disease agent. 16. A test kit as claimed in claim 14 wherein the specific binding agents are antibodies raised to a purified fraction obtainable by elution of the disease agent fraction from a DEAE-Sepharose CI ion -exchange column 17. A test kit as claimed in claim 16 wherein the antibodies are raised by administering the disease agent to an animal in the form of an immunogen conjugate. 18. A test kit as claimed in claim 17 wherein the conjugate is administered with an adjuvant or incomplete adjuvant. 19. A test kit as claimed in claim 16, 17 or 18 wherein the antibodies are labelled. 20. A test kit as claimed in claim 16 wherein the reagents comprise chemical reagents capable of specific reaction with the disease agent.

Inventors: EVEREST SALLY JANE, JACKMAN ROY, EVEREST, SALLY, JANE, JACKMAN, ROY
Applicants: EVEREST SALLY JANE, JACKMAN ROY, MINI AGRICULTURE & FISHERIES, EVEREST, SALLY, JANE, JACKMAN, ROY, THE MINISTER OF AGRICULTURE, FISHERIES AND FOOD IN
Application year: 1994
Main classification: G01N33
IPC codes: G01N33